In conventional mobile communication systems, communication quality is still subject to multi-path dispersion and temporal variation of communication channels. When a mobile terminal is in a high-mobility state, more multi-path dispersion and temporal variation of communication channels are introduced, which further degrades communication quality. Many kinds of technologies for improving communication quality have been disclosed. In order to deal with multi-path dispersion and temporal variation of communication channels produced when the mobile terminal is in a high-mobility state, special procedures and extra processes are necessary. However, existing mobile communication systems lack simple and convenient methods and apparatus for detecting whether a mobile terminal is in a high-mobility state or not. Usually, when whether a mobile terminal is in a high-mobility state or not is not known, various special procedures and extra processes are adopted to improve the communication quality. Due to lack of information on whether the mobile terminal is in a high-mobility state or not, existing mobile communication systems usually waste more power and computing resources, and also defer the communication procedures.
Specifically, the mobile radio channels in TD-SCDMA systems are easily subject to multi-path dispersion and temporal variation. To combat against the adverse effects due to the inter-symbol interference (ISI) introduced by multi-path dispersion, an equalizer is often used to perform channel equalization in the implementation of a receiver. Prior to performing channel equalization, channel impulse response (CIR) estimation must be finished. In TD-SCDMA systems, the CIR can be estimated by utilizing a training sequence (i.e., midamble). The training sequence consists of a number of known training symbols in a time slot. Besides the training symbols as a part of the training sequence, one time slot further includes two data fields and a guard period, as shown in FIG. 1. Strictly speaking, the estimated CIR is only valid over the duration of receiving the training sequence. Nevertheless, channel equalizers typically employ thus estimated CIR for channel equalization also on the data fields, under an implicit assumption that the temporal variation of the channels is so slow that the CIR can be regarded constant over a time slot on which channel equalization is performed. This assumption is reasonable in most communication scenarios where transmitters and/or receivers are stationary or are moving at a low speed. When transmitters and/or receivers are moving at a high speed, however, since the CIR changes considerably over a time slot, this assumption falls short. Therefore, the equalizer performance is degraded, and excessive errors are introduced during the stage of data demodulation.
A slot-based transmission approach (including TD-SCDMA systems) used to more accurately estimate the CIR for mobile communication systems is disclosed by H. Ishii and T. Ishiguro in U.S. patent application No. 2003/0185165A1, “System and Method of Interference Suppression,” published on Oct. 2nd, 2003 and assigned to NTT DoCoMo Inc. This patent application is incorporated herein by reference in its entirety. This prior art suggests a more accurate procedure, in which the CIRs are estimated for each time slot based on training sequences of these successive time slots and then interpolation is performed to obtain the instantaneous CIRs for data fields. Although a more accurate estimation of the CIRs for data fields can be obtained and hence a better system performance can be achieved, such procedure needs to perform an additional step of interpolation thereby consuming extra power. In addition, it is possible that time slots assigned to a user are not located in consecutive time slots in the data transmission in a TD-SCDMA system. In this case, the need to estimate the CIRs for adjacent time slots, which are not used for carrying data for this user, increases the power consumption of the receiver. For the above reasons, even if the aforesaid disclosure of U.S. patent application No. 2003/0185165A1 may yield an improvement in the system performance only in high-mobility scenarios, it is preferable to omit the additional step of interpolation so as to save power when the mobile terminal is in a low-mobility state. Especially when the receiver is located in the mobile terminal, it is more necessary to omit the additional step of interpolation, because saving power is very important for a mobile terminal.
For the above reasons, it is apparently necessary to detect whether a mobile terminal is in a high-mobility state or not.